The invention relates to an IC (integrated circuit) card system of the type in which IC cards are identified when they are connected to an external device such as a terminal. Throughout this specification and claims, the abbreviated term "IC" is used to denote integrated circuit.
IC cards containing IC circuits, in which personal identification numbers are prestored, have been used widely. When a business transaction is made using this IC card, the card is inserted in IC card terminal devices, such as those installed in banks or stores. The user keys in his personal identification number (PIN) using the keyboard of the terminal device. The terminal device compares the PIN read out from the IC card with the keyed in PIN. If these are coincident, the device determines that the terminal device in use is proper, and the IC card and its holder are both rightful and valid. Then, the business transaction is allowed.
However, the above IC card system in which the IC card is set to the terminal device to identify the PIN, suffers from some disadvantages. First of all, when the PIN is keyed in at the store, for example, there is a possibility that it will be memorized by someone watching the key-in operation. Secondary, there are terminal devices of a type in which the PIN keyed in by a card owner is stored upon receipt of a signal representing the coincidence between the keyed in PIN and the corresponding prestored one. In such a device, there is the danger that the PIN of the real card owner may be stolen by the owner of a shop, for example, equipped with this type of terminal device.
The first problem can easily be solved if the card owner carefully keys in his PIN so as not to have it stolen. As for the second problem, there is no counter-measure that can be taken by the card owner.
To cope with this problem, an improved IC card system is therefore proposed. At the time of issuing IC cards, the PIN of a card owner is stored in the card. The PIN keyed in from a keyboard on the card itself is compared with the corresponding stored one for PIN identification. The result of the identification is quickly displayed by a display window on the card. Thus, in this IC card system, the card holder can be identified using only the card, without any connection to the terminal device. This approach still involves the problem that the IC card itself could be duplicated. In this card system, if the display window shows "Real owner, OK", it is impossible to check if the card was issued by a valid card company, and it is very difficult to conclusively identify the real card owner. In this respect, there is no way, except by connecting the IC card to the external device, to identify the validity of the card.